Fluorination with granular crf3 catalyst



Patented Nov. 27, 1951 UNITED STATES;

PATENT OFFICE.

FLUORINATION WITH GRANULAR' CrFs CATALYST NfoDrawinga;v Application'November 13, 1947, Serial No. 785,812

invention relates ..to1 the catalytic vapor. phase fluorinationofaliphatic halo-organic compounds, and moreparticularly tola. catalyst'and". catalytic process for the vapor phase fluorination with hydrogen fluoride of halo-fluoro ethanes 'andl prop'anes."

F'luoro-ethanes and fluoro-propan'es sucli as CFLCFzCLCFaCI-IFz, CFaCFb and CFaiCEClLCFzCl would be:;valuable-,,-for-"such uses as refrigerants,- dielectric media, inert solvents.-and .selectiveesole vents in extraction operations if available commercially. However, these'compcunds have heretoiore been". made; ir1-v the? laboratory: only: by laborious means bythezuse .of stringentand; ex-- 4 v pensive? fluorinating; agents: such l as"; SbF's andtj metal perfiuorides; th'e=- latterrbeing -"made from metal' iluorides or Ychlorideswith elemental zfiuorine and not being economically feasible for room: mercialexploitation 'at therpresent timer; E1uoro--- meth'anes can be prepared":economically byvapor; phasereactionmoi-hydrogen;fluoride;with axhalo methane such asicarbon' tetrachloride .in;the prese ence..of a catalyst prepared by impregnating a. chromium halide onacarbon supportisuch as:. granular charcoal or' coke. Attempts .to. extend this type of reaction to 13118'fli101i11ati01h0fiha10- fiiioro ethanes and propanes have resulted inpoor organic recoveries and poor conversions to the desired products because of carboncarbon fission,- as will be shown herein.

It is an object of this invention to -provide an economical and 'commerc ally practicable process:- for preparing fluorinated eth'anesr andri propanes; It"'is-a further object to provideacatalyticwapor: phase process for reactinghydr'ogen fluoride with" balo-fiuoro ethanes orrpropanes to obtain fluorinated ethanes or propanesin good yields with high .organ c'recovery; Anotherzobject' is *tofl pro-.- vide a suitable catalyst for such 'aprocess. Other; objects will appear hereina'ftenf. 40

Iii-accordance with the'presentinvention it has beeniound thatan economical andcommercially practicable process for preparing fi'uorinated ethanes and'propanesfintgoodyields with high organic recoveries: comprisesreacting" a halo=- genated' aliphatic. hydrocarbonoffl to 3 carbon atoms, having at'least one. halogen atom other thanvfluorine, ,in thevapor phase with anhydrous" hydrogen fluoride in the presence of substantially carbonfree CrF catalyst attemperatures of 'from' 4 about 450 'CI to about 700"C.Qfo'r from about 1 to about seconds, and separating the fluori nated ethane or propane'irom the reactants and resulting reaction products;

It has been found that this process is only sucas 2 cessful when CrFa catalystris providedin ti-sub stantiallycarbon-free f0rm. This-is contrary tothe teaching'of the art regarding the production of fluoromethanes; and'the critical "efiectof car bon-on=theresults is surprising. In accordance: with'this invention a process of preparinghard refractory pellets of CrFs' catalyst'in' a substantially pureform suitable for --use intheabove-reaction comprises 'm'Xing' chromic fluoridewith,

polytetrafluoroethylene binder, pressing the-mix ture into pellets, and heating the pellets f in the presence of anhydrous hydrogen fluoride until? water and binder are removedi Halogenated aliphatic hydrocarbons-o1-2-7to 3* carbon-atomswhich may be employed as startingcompounds in the above process" include CFzCLCFiCl; CFCl.CHF2',' CFsCFClz'; CF3.CF'5C1; CFaCHZCI, CF3.CHC12, CF3.CFC1.CFC12 and corresponding compounds in which chlorine is' replaced by bromine or iodine.

Contrary to whatmight be expected, the-HF organic mole'ratio should'bek'ept as low as practi'ca-l; mole ratios of the-order 015:1 being-pref erable totl'iose-in the range 3:1; with-4:21 constituting the upper limit. This derives'from -the fact that} due to itslow' molecular-weight (20); the amount of HF used largely determines the contacttime, and for a given temperature and,

The; :contact times of the" reactantsrwith the: catalyst may be varied over aiwide'rangerof.about-1' 1 to about 60 seconds, depending upon the nature of the starting material, the reaction temperature and theayield desired. It isgenerally preferred to 'operate in-the regionof-lOto 30 seconds. The

use; of "atmospheric pressures is convenient;- but subatr'nospheric"and:superatmospheric' pressures maybe usedif'desired: The reaction'temperature used varies with :the compound-being *fluorinated and the product desired. When preparing CFaCEzClirom CF2C1.CF2C1 it is preferableato The-- catalyst may be prepared mixing;

powdered CrFa or CrlizBHzOwithsuflioientpoly tetrafiuoroethylene binderrto lubricate the pellet mold. and, retain the .chromic, fluoride, in. penet form after it'is pressed into shape. About 2% of and subsequently converted to chromic fluoride by treatment with hydrogen fluoride at high temperatures, but this ofiers no worthwhile ad tage.

In order to more clearly illustrate the invention, the preferred methods of carrying it into elfect and the advantageous results to be obtained thereby, the following examples are given:

Example 1 In the preparation of CIFs catalyst, 1690 parts of finely ground CrF3.3H2O were intimately mixed with 34 parts of finely pulverized polytetrafiuoroethylene and pressed into the shape of pellets x A". These pellets were placed in an unlined Inconel tube and heated slowly to 850 C. in an atmosphere of anhydrous hydrogen fluoride. Substantially all of the water of hydration and the polytetrafluoroethylene binder were thereby removed, leaving pure CrFs pellets, x which were quite hardand refractory and possessed high resistance to crushing. A catalyst bed of the pellets was provided extending for 22 inches of the 1.61 inch inside diameter by 45 inches long unlined Inconel tube reactor. temperature of the reactor was gradually raised to and then maintained at 480 C. to 500 C. by an electrically heated furnace, the temperature being measured by a thermocouple placed on the outside of the reactor tube. A mixture of anhydrous HF and CFzCLCFzCl (boiling point 3-4 C.) in the molal ratio of 2.1:1 was passed at atmospheric pressure through the reactor at a rate providing a contact time of 26-28 seconds with the catalyst bed. The reaction products were washed with water, passed through soda-lime and calcium chloride and finally condensed in traps cooled with solid CO2 in acetone and with liquid nitrogen. Analysis of the condensate showed the following composition:

Compound: Mol percent CFaCI 8.2 CF3.CF3 Trace CF3.CF2C1 38 CFzCLCFzCl 53.8

The organic recovery (of halogenated ethanes) was 91.8 mol percent.

Example 2 Compound: Mol percent CF3C1 8.8

CF3.CF3 9.2 CF3.CF2C1 47.5 CFzCLCFzCl 34.5

The organic recovery (of halogenated ethanes) was 91.2 mol percent.

Example 3 .A mixture of anhydrous HF and CEZQL-CE Cl The 4 in the molal ratio of 0.5 1 was passed through the reactor described in Example 1. With the reactor temperature maintained at 500 C. and with a flow rate such as to give a contact time of 10 seconds, the composition of the 'eflluent gases was as follows:

Compound: Mol percent CFsCl V 1.0 'CFsCFzCl 28.3 CFsCFs Nil CFzClCFzCl 68.0 High boilers 2.7

Organic recovery (of halogenated ethanes) was 96.3 mol percent.

Example 4 A mixture of anhydrous HF and CFzCLCI-IFz in the molal ratio of 2.2:1 was passed through the reactor described in Example 1, with the reactor temperature maintainedarat 550 C.-560 C. and at a rate providing an approximate catalyst contact time of 21-22 seconds. The effluent gases, treated in the manner described in Example I, had the following composition:

Compound: Mol percent Unidentified low boilers 10.2 CF3.CHF'2 14.5 CFzCLCHFz 75.3-

The organic recovery (of halogenated ethanes) was 89.8 mol percent. V

Example 5 A mixture of anhydrous HF and CF3.CFCl.CFCl-z in the molal ratio of 1.3:1 was passed through the reactor described in Example 1,'with the ICflO-r. tor temperature maintained at 445. C. and at a.

rate providing a catalyst contact time of 27-28 seconds. The liquid efiluent product was washed with ice water and ice-cold NaHCOa solution and dried by passage in the vapor phase over soda lime and anhydrous calcium chloride. The prod uct had the following composition:

Compound: M01 percent Unidentified products boiling at 78 C. to 76 C 0.5 CF3.CFC1.CF2C1 5.0 CF'3.CFC1.CFC12 94.5

The organic recovery, (of halogenated propanes) was 99.5 mol percent. I

The following examples show the deleterious effect which the presence of carbon has on the fluorination of chlorofluoroethanes in promoting carbon-carbon fission and in decreasing the conversion to desired products:

Example 6 The CIF3 catalyst bed of Example 1 was replaced by a 22 inch bed of activated carbon. In a manner similar to that of Example 1, a mixture of anhydrous HF and CFzCLCFzCl in a molal ratio of 2:1 was passed through the reactor, with the reactor temperature maintained at 443 C. and with a contact time of 26-27 seconds. The condensate, upon fractionation, showed a conversion to CF3.CF2C1 of only about 4% with an organic recovery (of halogenated ethanes) of 93.3%. An effort to increase the conversion by raising the temperature resulted in decrease in; organic recovery with slight increase in conversion to an extent which makes the method economically non-feasible.

Example 7 a. reaction similar to that of Example 5, a

mixture of .anhydrous HE .and.,CFzCl.CF-zCl inla molal ratio of 2:1 was passed through a catalyst bed consisting .of CrFa impregnated .on activated carbon, the amount of C1F3 being 10% of the weight of the carbon. The reactor was maintainedatlattemperaturecf 421 C. 721K123, contact time of 28-29 seconds was provided. The conversion to CF3.CF2C1 wasabout -'7.5% with-:an organic recovery :(of halogenated ,-ethanes) .of 84%. Raising the temperature of the reactor to 560-575 C. with an HF: organic ratio of 2.5:1 and a contact time of 18-19 seconds gave a conversion to CF3.CF2C1 of less than 12.5% and the organic recoverydropped to less than '75 .under these conditions, the .organic conversion and recovery are such that operation of this process is not economically feasible. On the other hand, an increase'in temperature when usingicarbon-free CrFs pelletsresults in nQJdr-op in -recovery...and increases the conversion to vdesired .products.

Example 8 In a reaction similar to. that described in Example 5, a mixture of anhydrousHF and in a molal ratio of 2:1 was passed through the catalyst bed of CrFa impregnated on activated carbon at a reactor temperature of 550-560 C. and with a contact time of 20-21 seconds. The effluent gases after washing, drying and condensation were subjected to fractionation. The conversion to CF3.CI-IF2 was about 10% and the organic recovery (of halogenated ethanes) was only 37%. The majority of the halogenated ethanes underwent pyrolytic decomposition.

The results of the above examples are summarized in the table.

Even I tegratingaction ofthe. hydrogen fluoride. O rganic fibers, metallized cotton, wool, etc., .are also recluded .since. they .are..not capable -of withstanding the hightemperatures involved. The use of salts as binders is also believed .to be. preeluded because of deleterious catalytic efiect of most .of them on the. organic compounds or -because .of complete disintegration of.pellets made with. .salt binders at temperatures far below. the

temperatures requiredforthe .fiuorination. 0rganic binders, such ..as. .g'lycerine, sugar,- starch,

etc., arenot successful since they w'illnot .withstand the combined action of hydrogen fluoride and high temperatures,pundergoing decomposition with deposition of deleterious carbon on the pellets.

Thepresentinvention provides'a catalyst and a. process for utilizing the catalyst *valuable for' the preparation 'of highly fluori-nated ethanes and catalyst and usually with disintegration of the and CFaCFCLCFiCl, which are not obtainable by the usual-commercial methodsof fluorination, e. g., with antimony chlorofluorides. The process is economical and commercially practicable because of its simplicity, the good yields of desired products and the high organic recoveries.

The

catalyst is provided in a highly stable and usable form which is free from deleterious materials and from carriers or binders which cannot withstand involved.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is the hydrogen fluoride and. high temperatures Reactor C Iontact BRJolaI C d Fl (firganic Conversions to the Following Compounds in M01 Per Cent ime, atio ompoun uoecov- Type of Catalyst 98" in Sec- HF: rinated cry, M01

1 ends Org. Per Cent CFQCFI CF cF Cl CFQCHF, CFQCFCICFgC] OrFa pellets 26-28 2. 1 CF2G]CF2CL 91. 8 Trace 38 Do 15-16 3. 7 CFQCICFZCI- 91.2 9.2 47.6 Do. 10 0.5 OF2C1CF201... 96. 3 Nil 28. 3 Do 21-22 2. 2 CFgClCHFz 89.8 14. 5 Do 27-28 1.3 CFZCFCICFChU 99. 5 5.0 Activated carbon. 26-27 2 CFZOIOFQOI 93. 3 4 GrFr-carbon 421 28-29 2 CF C1CF CL 84 7. Do 560-575 18-19 2. 5 CFZCIOFZOL. 75 12. D0 550-560 20-21 2 CFgClOHFz 37 A comparison of the results given in the table shows the marked superiority of the CrFs pellets of the present invention over CrFa impregnated on a carbon support. Under similar operating conditions superior conversions and an overwhelming superiority in practically eliminating pyrolysis of the organic compounds is obtained. In addition to causing carbon-carbon fission resulting in poor organic recoveries, the pyrolysis causes a rapid loss of catalyst activity with increasingly poor conversions. These disadvantages have been effectively overcome through the use of the specially prepared and pretreated CrFa pellets under the reaction conditions of the present invention. Furthermore, in the event that carbon deposition takes place on the CI'Fs pellets, which would then catalyze carbon-carbon fission, the deleterious carbon may be removed by burning with air or oxygen without unduly affecting the original catalyst activity.

The use of other supports or carriers for CrF3,

instead of carbon, appears to be precluded by the 75 to be understood that the invention is not limited fined in the appended claims.

What is claimed is: l. The process of preparing a fluorinated aliphatic organic compound which comprises reactto the specific illustrations thereof except as deing a halogenated aliphatic hydrocarbon of 2 to 3 carbon atoms, having at least one halogen atom other than fluorine, in the vapor phase with anhydrous hydrogen fluoride in the presence of hard refractory pellets consisting of substantially pure CrFs catalyst at temperatures of from about 450 C. to about 700 C. and separating the fiuorinated compound.

2. The process of preparing a fluorinated aliphatic organic compound which comprises reacting a halogenated aliphatic hydrocarbon of 2 ly pure CrFa catalyst at temperatures of from about 450 C. to about 700 C. for from about 10 to about 30 seconds, and separating the fluorinated compound.

3. The process of preparing a fluorinated aliphatic organic compound which comprises reacting a halogenated aliphatic hydrocarbon of 2 to 3 carbon atoms, having at least one halogen atom other than fluorine, in the vapor phase with anhydrous hydrogen fluoride in a molal ratio of hydrogen fluoride to halogenated hydrocarbon of from about 0.521 to about 3:1 in the presence of hard refractory pellets consisting of substantially pure C1F3 catalyst at temperatures of from about 450 C. to about 700 C. and separating the fluorinated compounds.

4. The process of preparing CF'3.CF3 which comprises bringing mixed vapors of HF and into contact with hard refractory pellets consisting of substantially pure CrFa catalyst at a temperature of about 600 C. to 700 C. and separating the CF3.CF3 formed.

5. The process of preparing CF3.CF2C1 which comprises bringing mixed vapors of HF and CFzCLCFzCI into contact with hard refractory pellets consisting of substantially pure CrFs cat- 8 alyst at a temperature of about 450 C. to about 550 C. and separating the CF3.CF2C] formed.

6. The process of preparing CF3.CHF2 which comprises bringing mixed vapors of HF and REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,937,885 Gitzen et al. Dec. 5, 1933 2,110,369 Leicester Mar. 8, 1938 2,400,446 Veltman -1 May 14, 1946 2,461,523 Cofiman et a1. Feb. 15, 1949 OTHER REFERENCES Catalysis, Berkman et al., pub. by Reinhold Pub. Corp., N. Y. (1940), page 426. 

1. THE PROCESS OF PREPARING A FLUORINATED ALIPHATIC ORGANIC COMPOUND WHICH COMPRISES REACTING A HALOGENATED ALIPHATIC HYDROCARBON OF 2 TO 3 CARBON ATOMS, HAVING AT LEAST ONE HALOGEN ATOM OTHER THAN FLUORINE, IN THE VAPOR PHASE WITH ANHYDROUS HYDROGEN FLUORIDE IN THE PRESENCE OF HARD REFRACTORY PELLETS CONSISTING OF SUBSTANTIALLY PURE CRF3 CATALYST AT TEMPERATURES OF FROM ABOUT 450* C. TO ABOUT 700* C. AND SEPARATING THE FLUORINATED COMPOUND. 